Bottom Line:
The lungs of ECTV-infected Fas- and FasL-deficient mice showed significant inflammation during later phases of infection accompanied by decreased expression of anti-inflammatory IL-10 and TGF-β1 cytokines and disturbances in CXCL1 and CXCL9 expression.Experiments in vitro demonstrated that ECTV-infected cultures of epithelial cells, but not macrophages, upregulate Fas and FasL and are susceptible to Fas-induced apoptosis.Our study demonstrates that Fas/FasL pathway during ECTV infection of the lungs plays an important role in controlling local inflammatory response and mounting of antiviral response.

ABSTRACTFas receptor-Fas ligand (FasL) signalling is involved in apoptosis of immune cells as well as of the virus infected target cells but increasing evidence accumulates on Fas as a mediator of apoptosis-independent processes such as induction of activating and proinflammatory signals. In this study, we examined the role of Fas/FasL pathway in inflammatory and antiviral response in lungs using a mousepox model applied to C57BL6/J, B6. MRL-Faslpr/J, and B6Smn.C3-Faslgld/J mice. Ectromelia virus (ECTV) infection of Fas- and FasL-deficient mice led to increased virus titers in lungs and decreased migration of IFN-γ expressing NK cells, CD4+ T cells, CD8+ T cells, and decreased IL-15 expression. The lungs of ECTV-infected Fas- and FasL-deficient mice showed significant inflammation during later phases of infection accompanied by decreased expression of anti-inflammatory IL-10 and TGF-β1 cytokines and disturbances in CXCL1 and CXCL9 expression. Experiments in vitro demonstrated that ECTV-infected cultures of epithelial cells, but not macrophages, upregulate Fas and FasL and are susceptible to Fas-induced apoptosis. Our study demonstrates that Fas/FasL pathway during ECTV infection of the lungs plays an important role in controlling local inflammatory response and mounting of antiviral response.

fig2: Lack of Fas or FasL leads to disturbances in the inflammatory response. (a) Histological analysis of lungs isolated from ECTV-infected Fas (−), FasL (−), and WT (C57BL/6) mice at 7 and 10 days of infection and uninfected controls. The nuclei were counterstained with Harris haematoxylin (violet) (×40 and 100). Total counts of alveolar macrophages (b) and inflammatory monocytes (b) in cell suspensions prepared from the lungs isolated from Fas (−), FasL (−), and WT (C57BL/6) mice at 3, 7, 10, and 14 days of ECTV infection and from control, uninfected mice. The bars represent the mean from 5 separate experiments ± SEM. *Significant differences with P ≤ 0.05 and **P ≤ 0.01 in comparison to wild-type mice.

Mentions:
To study the involvement of Fas-dependent pathway during ECTV infection of lungs, we used a well-established model of intranasal infection of C57BL6 mice. In the lungs of uninfected C57BL6 mice, Fas expression was detected on the epithelial cells of bronchial epithelium and single alveolar macrophages, while FasL expression was undetectable (Figure 1(a)). During the peak of ECTV infection in the lungs at day 7 after infection (p.i.), Fas expression was found on the bronchial epithelial cells but predominantly on the alveolar macrophages in the area surrounding bronchia, while FasL-positive cells were detected as mostly of monocyte and epithelial origin (Figure 1(a)). To elucidate the role of Fas/FasL pathway during ECTV infection, we infected Fas- and FasL-deficient mice intranasally with 5 × 103 PFU of ECTV-MOS, which was about a 60% lethal dose for C57BL6 mice (WT). Mice of all three tested strains showed mortality already at day 5 p.i., however, later during infection significantly more Fas (−) and FasL (−) mice died in comparison to the wild-type strain (P ≤ 0.001) (Figure 1(b)). RT2-PCR method was used to measure ECTV DNA titers in the lungs collected at 3rd, 7th, 10th, and 14th d.p.i.; the results showed significantly increased titers of ECTV in the lungs of Fas- and FasL-deficient mice at all tested time points (P ≤ 0.05) (Figure 1(c)). The highest viral titers in the lungs of wild-type mice were detected at 7th d.p.i. but the titers of ECTV in Fas (−) and FasL (−) mice were significantly higher in comparison to wild-type mice during all tested period (P ≤ 0.001) (Figure 1(c)). Histopathologic examination of the lung tissue isolated from all tested mice strains at day 7 of ECTV infection revealed inflammatory and necrotic lesions in the epithelia of lung bronchioles (Figure 2(a)). However, the lungs of Fas- and FasL-deficient mice showed more inflammatory lesions in the area surrounding bronchia (Figure 2(a)). The inflammatory lesions observed in Fas- and FasL-deficient mice were necrotic and still present at day 10 of infection in comparison to the lung tissue of wild-type mice (Figure 2(a)). To investigate the kinetics and extent of the inflammatory reaction in lungs, we prepared single cell suspensions and analysed by flow cytometry for the total counts of alveolar macrophages and inflammatory monocytes (Figures 2(b) and 2(c)). The total numbers of alveolar macrophages (CD11c+/CD11b−/MHCIIlow) in the lungs of all tested strains increased significantly at 3rd and 7th d.p.i., to subsequently decrease at 14th d.p.i. in comparison to uninfected control mice (P ≤ 0.05) (Figure 2(b)). When comparing to ECTV-infected wild-type mice, both Fas- and FasL-deficient mice at 7th and 10th d.p.i. showed significantly increased total counts of alveolar macrophages (P ≤ 0.05) (Figure 2(b)). Assessment of inflammatory monocytes (CD11b+/CD11c−/MHCII−) in the lungs of ECTV-infected mice revealed that the total counts of inflammatory monocytes were significantly increased during the whole infection period (P ≤ 0.05) (Figure 2(c)). However, the wild-type mice showed significantly higher total counts of inflammatory monocytes at 3rd d.p.i. in comparison to Fas- and FasL-deficient mice (P ≤ 0.001) (Figure 2(c)). Later during infection (7th, 10th, and 14th d.p.i.), Fas- and FasL-deficient mice showed an opposite effect with a more significant inflammatory reaction in comparison to wild-type mice (P ≤ 0.05) (Figure 2(c)).

fig2: Lack of Fas or FasL leads to disturbances in the inflammatory response. (a) Histological analysis of lungs isolated from ECTV-infected Fas (−), FasL (−), and WT (C57BL/6) mice at 7 and 10 days of infection and uninfected controls. The nuclei were counterstained with Harris haematoxylin (violet) (×40 and 100). Total counts of alveolar macrophages (b) and inflammatory monocytes (b) in cell suspensions prepared from the lungs isolated from Fas (−), FasL (−), and WT (C57BL/6) mice at 3, 7, 10, and 14 days of ECTV infection and from control, uninfected mice. The bars represent the mean from 5 separate experiments ± SEM. *Significant differences with P ≤ 0.05 and **P ≤ 0.01 in comparison to wild-type mice.

Mentions:
To study the involvement of Fas-dependent pathway during ECTV infection of lungs, we used a well-established model of intranasal infection of C57BL6 mice. In the lungs of uninfected C57BL6 mice, Fas expression was detected on the epithelial cells of bronchial epithelium and single alveolar macrophages, while FasL expression was undetectable (Figure 1(a)). During the peak of ECTV infection in the lungs at day 7 after infection (p.i.), Fas expression was found on the bronchial epithelial cells but predominantly on the alveolar macrophages in the area surrounding bronchia, while FasL-positive cells were detected as mostly of monocyte and epithelial origin (Figure 1(a)). To elucidate the role of Fas/FasL pathway during ECTV infection, we infected Fas- and FasL-deficient mice intranasally with 5 × 103 PFU of ECTV-MOS, which was about a 60% lethal dose for C57BL6 mice (WT). Mice of all three tested strains showed mortality already at day 5 p.i., however, later during infection significantly more Fas (−) and FasL (−) mice died in comparison to the wild-type strain (P ≤ 0.001) (Figure 1(b)). RT2-PCR method was used to measure ECTV DNA titers in the lungs collected at 3rd, 7th, 10th, and 14th d.p.i.; the results showed significantly increased titers of ECTV in the lungs of Fas- and FasL-deficient mice at all tested time points (P ≤ 0.05) (Figure 1(c)). The highest viral titers in the lungs of wild-type mice were detected at 7th d.p.i. but the titers of ECTV in Fas (−) and FasL (−) mice were significantly higher in comparison to wild-type mice during all tested period (P ≤ 0.001) (Figure 1(c)). Histopathologic examination of the lung tissue isolated from all tested mice strains at day 7 of ECTV infection revealed inflammatory and necrotic lesions in the epithelia of lung bronchioles (Figure 2(a)). However, the lungs of Fas- and FasL-deficient mice showed more inflammatory lesions in the area surrounding bronchia (Figure 2(a)). The inflammatory lesions observed in Fas- and FasL-deficient mice were necrotic and still present at day 10 of infection in comparison to the lung tissue of wild-type mice (Figure 2(a)). To investigate the kinetics and extent of the inflammatory reaction in lungs, we prepared single cell suspensions and analysed by flow cytometry for the total counts of alveolar macrophages and inflammatory monocytes (Figures 2(b) and 2(c)). The total numbers of alveolar macrophages (CD11c+/CD11b−/MHCIIlow) in the lungs of all tested strains increased significantly at 3rd and 7th d.p.i., to subsequently decrease at 14th d.p.i. in comparison to uninfected control mice (P ≤ 0.05) (Figure 2(b)). When comparing to ECTV-infected wild-type mice, both Fas- and FasL-deficient mice at 7th and 10th d.p.i. showed significantly increased total counts of alveolar macrophages (P ≤ 0.05) (Figure 2(b)). Assessment of inflammatory monocytes (CD11b+/CD11c−/MHCII−) in the lungs of ECTV-infected mice revealed that the total counts of inflammatory monocytes were significantly increased during the whole infection period (P ≤ 0.05) (Figure 2(c)). However, the wild-type mice showed significantly higher total counts of inflammatory monocytes at 3rd d.p.i. in comparison to Fas- and FasL-deficient mice (P ≤ 0.001) (Figure 2(c)). Later during infection (7th, 10th, and 14th d.p.i.), Fas- and FasL-deficient mice showed an opposite effect with a more significant inflammatory reaction in comparison to wild-type mice (P ≤ 0.05) (Figure 2(c)).

Bottom Line:
The lungs of ECTV-infected Fas- and FasL-deficient mice showed significant inflammation during later phases of infection accompanied by decreased expression of anti-inflammatory IL-10 and TGF-β1 cytokines and disturbances in CXCL1 and CXCL9 expression.Experiments in vitro demonstrated that ECTV-infected cultures of epithelial cells, but not macrophages, upregulate Fas and FasL and are susceptible to Fas-induced apoptosis.Our study demonstrates that Fas/FasL pathway during ECTV infection of the lungs plays an important role in controlling local inflammatory response and mounting of antiviral response.

ABSTRACTFas receptor-Fas ligand (FasL) signalling is involved in apoptosis of immune cells as well as of the virus infected target cells but increasing evidence accumulates on Fas as a mediator of apoptosis-independent processes such as induction of activating and proinflammatory signals. In this study, we examined the role of Fas/FasL pathway in inflammatory and antiviral response in lungs using a mousepox model applied to C57BL6/J, B6. MRL-Faslpr/J, and B6Smn.C3-Faslgld/J mice. Ectromelia virus (ECTV) infection of Fas- and FasL-deficient mice led to increased virus titers in lungs and decreased migration of IFN-γ expressing NK cells, CD4+ T cells, CD8+ T cells, and decreased IL-15 expression. The lungs of ECTV-infected Fas- and FasL-deficient mice showed significant inflammation during later phases of infection accompanied by decreased expression of anti-inflammatory IL-10 and TGF-β1 cytokines and disturbances in CXCL1 and CXCL9 expression. Experiments in vitro demonstrated that ECTV-infected cultures of epithelial cells, but not macrophages, upregulate Fas and FasL and are susceptible to Fas-induced apoptosis. Our study demonstrates that Fas/FasL pathway during ECTV infection of the lungs plays an important role in controlling local inflammatory response and mounting of antiviral response.